This invention relates to an electrochemical system utilizing an electrochemical cell and more particularly to a thermally regenerative electrochemical system utilizing one or more electrochemical cells having water-based electrolytes containing salts of a multivalent metal whose respective order of potentials for a pair of its redox couples is reversible.
Thermally regenerative electrochemical systems have some similarities to secondary batteries except that the regeneration of the electrochemically active electrode reactants is accomplished thermally rather than electrically. They may also be considered as devices to convert or upgrade thermal energy to electrical energy and advantageously include chemical storage means for storing the energy until needed for electrical purposes.
Previously, thermally regenerative electrochemical systems have been characterized by a number of limitations. In some systems, the regeneration has involved the chemical decomposition of the reaction products to produce the initial reactants as disclosed in U.S. Pat. Nos. 3,536,530 and 936,980. Other systems have been regenerated by the distillation of a salt to provide two electrolytes of differing concentrations as in U.S. Pat. No. 4,292,378. Photoelectric devices have also been utilized to produce electricity to electrically generate electrolytes at lower temperatures but this has been limited by the cost and limited power associated with these devices.
Particularly with some systems associated with the chemical decomposition of the reaction products, the regeneration temperatures, energy requirements and corrosive conditions have been substantial. In many instances, the regeneration temperatures have been at least about 500.degree. C. and often in excess of 500.degree. C. In U.S. Pat. No. 3,536,530, the temperature of regeneration to form the initial chemical reactants is about 550.degree. C. For a lithium hydride system as described in "The Encyclopedia of Electrochemistry", Hampel (ed.), 1964, p. 619, the regeneration temperature is about 900.degree.-1200.degree. C.
Since the cost of operating these regenerative electrochemical systems is dependent on the cost of the energy to regenerate the initial electrolytes for the electrochemical cell, attention has been directed to lower cost energy sources. One convenient source is heat available from low grade heat sources such as solar collectors or from industrial operations which provide heat at temperatures below 400.degree. C. and often below about 200.degree. C. While these sources of heat have cost advantages, the temperatures have usually been below those required for many regenerative systems.
Accordingly, one object of this invention is a new regenerative electrochemical system with advantages over those previously known. Another object is a regenerative electrochemical system in which regenerative energy is not utilized to decompose the reaction products to reform the initial electrolytes. A second object of the invention is a regenerative electrochemical system which does not require distillation of the metal salt in the electrolytes. An additional object of the invention is a thermally regenerative electrochemical system. Yet another object of the invention is a thermally regenerative electrochemical system in which the regeneration temperature is below about 400.degree. C. and preferably below 200.degree. C.